please confirm my simple LED project working

[cpteoh26]

simple led projects

hi all.
i am making a simple LED project for my children..
i use super bright LED which consume 25-30mA
the super bright LED forward voltage is about 2.7v-3.0v.
would my circuit below work? thanks.



please confirm i am correct for my think below.
a) i use 60 Ohm, 5 Watt resistor to limit the current to 200mA
by theory calculation, square(200mA) x 60 Ohm = 2.4 Watt, i use double rating of resistor for safety propose.

b)i assume the current will be divide equally to each LED. i mean, each LED will be taking 200mA/7 (7 LED in my circuit). which is about 28.5mA. am i correct for current divide equally theory?

c)assume the 12Vdc power jack up 10% to 13.2Vdc, my current would be 220mA, each LED is taking 31.4mA, but should be still ok with the LED?

d) LED is current driven component, 12Vdc should have no problem on it. correct? it is NOT necessary to supply normal 5Vdc, correct?

e)with the LED forward voltage 2.7-3.0V, my current calculation should be (12-2.7) V / 60 Ohm?? is it i should use ((12Vdc) - (forward voltage for LED)) / (Resistor) ??

thanks.

 

[pauloynski]

led 30ma life

One problem with your project is assuming that the current will divide equaly. Since this is not the case, the ones with larger current may suffer low reliability. A much better solution is to feed any led with an individual resistor, in this case (as in any other) you should know the voltage across the led at nominal current. Red=1,9V, Green=2,3V and Blue=White=3,6V (may differ depending on brand and manufacturing process). So, assuming a GREEN led, you should place a resistor of: R= (12-2,3)/30mA = 323==> 330Ω for each one. Power should be 0,28W minimum. You can also think of constructing sets of series connected leds to decrease power consumption. Just make, for example, 2 sets of 3 green leds series connected, and adjust the value of the resistors accordingly. You´ll save 66% of power. If you´re using blue or white leds make sets of 2 leds.

 

[cpteoh26]

simple led

One problem with your project is assuming that the current will divide equaly. Since this is not the case, the ones with larger current may suffer low reliability. A much better solution is to feed any led with an individual resistor, in this case (as in any other) you should know the voltage across the led at nominal current. Red=1,9V, Green=2,3V and Blue=White=3,6V (may differ depending on brand and manufacturing process). So, assuming a GREEN led, you should place a resistor of: R= (12-2,3)/30mA = 323==> 330Ω for each one. Power should be 0,28W minimum. You can also think of constructing sets of series connected leds to decrease power consumption. Just make, for example, 2 sets of 3 green leds series connected, and adjust the value of the resistors accordingly. You´ll save 66% of power. If you´re using blue or white leds make sets of 2 leds.

how about yellow, orange LED? what is the voltage across for them?

 

[pauloynski]

resistor in simple led projects

Yellow=2.1V but the difference from red to green is so small that you need not to take into it consideration when using a large suplly voltage as 12V.

Added after 4 minutes:

Some ROC made leds are not reliable at 30mA. 20mA would be a better choce.

 

[AVM_NOIDA]

individual resistor led

Hi

Since you are using a 12Volts supply, hence as suggested better way would be to add the LEDs in series and use a lesser wattage resistor or use LM317 in current control mode (Please see the datasheet).

We had used LM317 in similar application and it worked ok.

Due to semiconductor characteristic the LED voltage will vary with temperature and current.

Thanks

 

[dhrubadey]

simple project by resistor

Hi cpteoh26, This resistance is not good for the life of L.E.Ds. you use 10 resistor 470ohms 1/4watt, and connect it serially with each L.E.D.
Thanks